Java：自动找到具有main方法的类

Question

Is there a way to tell jvm to look for a class with entry main method automatically rather than to specify it when invoking java ClassWithMainMethod ?

In other words, I have directory with many compiled classes one of which has main method and I want to only specify that directory.

Answer 1

No, there is no way to do that. You can create an executable jar, and define what the main class is in the jar manifest, allowing you to use

java -jar MyJar.jar

though.

See http://docs.oracle.com/javase/tutorial/deployment/jar/appman.html

You may also deliver your app with a script which executes the appropriate command for you:

#startup.cmd
java -cp ... com.foo.bar.Main

Answer 2

If, in your scenario:

• it is okay to execute the first classfile in a directory;
• the classes in this directory are in the default package;
• the javap command is available – ie you've got a JDK installed, not just a JRE;

you could use the following bash script:

#!/usr/bin/env sh
for classfile in *.class; do
    classname=$(echo $classfile | cut -f 1 -d '.')
    echo $classname
    if javap -public $classname | fgrep 'public static void main(java.lang.String[])'; then
        java $classname "$@"
    fi
done

Answer 3

如果您的应用程序位于.jar文件中，则可以在其清单中指定主类

Answer 4

If there are more then one class with main method?

I think you can create a executable Jar file and specify class having main function in manifest file. So, whenever user will run jar file. Class with main function will be executed.